Generally in analysis of samples, such as in analysis of environmental samples such as soil, water, fly ash, tissue or other materials, for trace residues of analytes of interest from matrices it is common to extract and then enrich or concentrate the content of the analytes in order to achieve better detection sensitivity. Among the enrichment methods commonly used there may be mentioned, for example, simple concentration of a dilute solution containing organic analytes by reducing the content of the solvents; liquid-liquid or liquid-solid (solid phase) extraction, generally followed by concentration of the extracts; gas-solid extraction or purge and trap methods, generally followed by desorption of analytes from solids or traps; leeching/extracting of analytes from solid samples with an organic solvent using techniques such as those employing a SOXHLET apparatus; and supercritical fluid extractions.
However, the use of organic solvents present problems of disposability, toxicity and the like. Therefore, recently a solid phase microextraction (SPME) process was developed by Janusz Pawliszyn of the University of Waterloo, Ontario, Canada, to eliminate solvent usage. The SPME process and apparatus therefor is disclosed for example in International Patent (PCT) Publication WO 91/15745 of J. Pawliszyn, published Oct. 17, 1991, and incorporated herein by reference thereto.
In said SPME process, a coated or uncoated fiber housed within a needle of a syringe is brought into contact with components/analytes in a fluid carrier or headspace above the carrier for a sufficient period of time for extraction of the analytes to occur onto the fiber or coated fiber. Subsequently the fiber is removed from the carrier or headspace above the carrier and the analytes desorbed from the fiber generally by thermal desorption into an analytical instrument, such as a gas chromatograph (GC), for detection and quantification of the analytes.
SPME has been shown to be a very useful sample preparation technique for a variety of analytes. However, SPME extraction and detection has some very serious limitations. One particularly serious limitation is in relation to attempting to utilize SPME for extractions of trace organic analytes in organic solvent carrier matrices. Basically, SPME generally cannot be applied to extraction of trace amounts of organic analytes from organic solvent carrier matrices, such as hexane. Attempts to apply SPME to extraction of trace amounts of organic analytes from organic solvents carrier matrices do not provide acceptable results because the solvent matrix is extracted by the coated fiber of the SPME device. SPME fibers for extraction of organic analytes are generally coated with an organic phase, such as the non-polar poly(dimethylsiloxane) (PDMS). Instead of the trace organic analytes being adsorbed on or into the organic phase coating on the fiber, the solvent carrier matrix components are themselves adsorbed or extracted onto the organic phase due to their overwhelmingly predominant presence in the sample. This prevents selective, efficient extraction of the trace organic analytes. For this reason SPME has not found any practical applicability for extraction of trace organic analytes from organic solvent carrier matrices. Rather, SPME carrier matrices have generally comprised predominantly aqueous matrices, for example water, a water-methanol (95:5) matrix or an aqueous inorganic salt solution matrix.
This is a particularly serious limitation on the use of SPME extraction procedure since many common sample enrichment and preparation techniques for organic analysis and detection of trace amounts of organic analytes in a sample involve contacting the sample with an organic solvent carrier matrix to dissolve the organic analytes in the organic solvent carrier matrix, or in some way extracting the trace organic analytes into an organic solvent carrier matrix. For example, United States Environmental Protection Agency (EPA) Methods 608 and 525.1 require liquid-liquid extraction or liquid-solid extraction of semivolatile organic compounds, such as pesticides and polyaromatic organic compounds, from aqueous samples, such as municipal and industrial discharges or drinking water, into organic solvents. Organic solvents are used because the organic solvents have a high dissolution capability/power for the organic analytes. Subsequent concentration of the extracts and analysis thereof can give reasonable good detection. However, detection sensitivity is not particularly good and generally detection of trace amounts of less than 1 ppb are difficult or impossible to obtain with a mass spectrometer. Moreover, attempts to apply SPME methodology to this type of analysis for trace organic analytes in an organic solvent carrier matrix have failed to give selective extraction of the trace organic analytes out of the organic solvent carrier matrix due to the overwhelmingly predominant presence of said organic solvent carrier matrix as mentioned hereinbefore.